The thing that would make the most improvement would be the video card and it would only be realized when playing a game and of course it would depend on how much extra cash you had. This is still a 560Ti but it is the 448 cores one.
EVGA 012-P3-2068-KR GeForce GTX 560 Ti (Fermi) 448 Cores Classified 1280MB 320-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
High Current Pro HCP-850 850W TX12V v2.3 / EPS12V v2.92 SLI Certified CrossFire Certified 80 PLUS GOLD Certified Modular Active PFC Power Supply
Since we're spending more money , why not get a little more power?
Corsair Force Series GT CSSD-F120GBGT-BK 2.5" 120GB SATA III Internal Solid State Drive (SSD)
$194.99 and a $30 rebate makes it $164.99http://www.newegg.com/Product/Product.aspx?Item=N82E16820233191
Everyone has thier opinion on the best SSD and mine is this.
Other than that call in your order.